1. Technical Field
The present invention relates to a technology of driving a capacitive load having a fluctuating capacitive component and a technology of switching and driving plural capacitive loads having different capacitive components.
2. Related Art
There are lots of actuators that perform operations of injecting liquids when predetermined drive signals are applied thereto like injection heads mounted on inkjet printers. Since the operation of the actuator depends on a voltage applied thereto, in order to sufficiently get the performance of the actuator, it is desirable that a higher voltage may be applied. For the purpose, a drive waveform signal to be applied to the actuator is power-amplified and applied to the actuator.
As a method of power-amplifying the drive waveform signal, for example, a method using a class D amplifier is known (JP-A-2005-329710 or the like). In this method, power amplification is performed after the drive waveform signal is pulse-modulated and converted into a pulsed modulated signal. As a pulse modulation system, either of the pulse width modulation (MCOM) system or the pulse density modulation (PDM) system may be applied and the pulse width modulation is typically used. By power-amplifying the obtained pulsed modulated signal, the signal is converted into a pulsed modulated signal (amplified digital signal) that changes between the power supply voltage and the ground, and then, by removing the modulated component using a low pass filter, a power-amplified drive waveform signal (drive signal) is generated.
A class E amplifier used for power amplification in the radio-frequency range (RF) is also known. In the class E amplifier, power amplification is performed utilizing a resonance phenomenon occurring between inductance of an inductive element and capacitance of a capacitive load, and thus, a voltage exceeding the power supply voltage may be generated.
However, in the above described related art, there has been a problem that it is impossible to generate a drive signal by amplifying a drive waveform signal to a voltage equal to or more than the power supply voltage or stably generate the drive signal without being affected by the ambient temperature, the element temperature, and manufacturing variations. For example, in the class D amplifier, the voltage is changed by changing the duty ratio of the pulsed modulated signal, and the voltage may be changed only between the duty ratio of 0% corresponding to the ground and the duty ratio of 100% corresponding to the power supply voltage. In addition, to realize the duty ratio of 100% by pulse width modulation, a pulse having an infinitely narrow width is necessary, however, the pulse width that can be output has a limitation and, actually, it is impossible to amplify the voltage to the power supply voltage. Further, in the case of pulse density modulation, the voltage can be amplified to the power supply voltage, however, apart at a low generation frequency of pulse appears and the pulse component may not sufficiently be removed by a low pass filter in this part, and thus, the obtained drive signal is distorted.
Furthermore, in the class E amplifier, the power amplification is performed utilizing a resonance phenomenon (LC resonance) occurring between inductance L of an inductive element and capacitance C of a capacitive load, however, the frequency at which resonance is generated (resonance frequency) changes due to influences of the ambient temperature, the element temperature change, or manufacturing variations of the elements. Since the LC resonance has a high Q-value, when the resonance frequency changes, gain largely changes. Accordingly, it is impossible to generate a drive signal by stably power-amplifying a drive waveform signal.